The present invention relates to a transformer, particularly to a technology of improving direct current magnetic deviation of a core.
According to a transformer connected with a thyristor or the like on a primary side or a secondary side thereof, there is frequently a case in which direct current magnetic deviation is caused in a core. The direct current magnetic deviation is a phenomenon in which magnetic flux passing through a core is deviated to a side of positive or negative polarity on a B-H characteristic (characteristic of B-H curve) as a result of generating a direct current component in a coil. FIG. 1 is an explanatory view of the direct current magnetic deviation when a load 4 such as a thyristor is connected to a secondary side of a transformer. As shown by FIG. 1, when voltage V1 in a shape of a sine wave is applied to, for example, a primary side winding 2, voltage in a shape of a sine wave is induced at a secondary side winding 3 and current i2 subjected to half-wave rectification by the load 4 flows and forms a direct current component level shown by a dotted line. The direct current component level of the current generates a magnetic field deviated to a positive or negative side (positive side in the drawing) and excites a core 1 in a state of being deviated to one side on a B-H characteristic (characteristic of B-H curve) (direct current magnetic deviation). When the direct current magnetic deviation is caused, loss such as hysteresis loss in the core is increased. Further, in many cases, the core 1 reaches a magnetically saturated state by the direct current magnetic deviation, harmonic components are generated also in magnetostriction and vibration or noise is also increased. Further, depending on cases, excessively large current flows in the primary side winding, which destructs an element or the like connected thereto.
As a measure of restraining the direct current magnetic deviation of the transformer, a technology of bringing the B-H characteristic of the core into an unsaturated characteristic as shown by a curve 6 in FIG. 2, is effective. A curve 5 shown for comparison is substantially a characteristic curve of a general core. By widening a range of magnetic field strength having the B-H characteristic shown by the unsaturated characteristic as in the curve 6, an amount of a change of magnetic flux in the case of causing the unsaturated B-H characteristic can be reduced. Conventionally, in order to realize the unsaturated B-H characteristic, (1) magnetic flux density is reduced by increasing a sectional area of the core or (2) the magnetic flux amount is restrained by increasing reluctance of a magnetic circuit by providing a gap portion in the magnetic circuit of the core. (2) is described in, for example, Japanese Patent Laid-Open No. 222454/1996. According to (1) of the prior art, since an amount of the core member is increased, volume or weight of the transformer is increased and the cost is also increased. Depending on cases, iron loss is also increased. Further, (2) gives rise to a reduction in core strength or an increase in noise by magnetic suction force operated at the gap portion. Particularly, in the case of a three-phase transformer, there is brought about a drawback in which excitation characteristics of respective phrases differ by a dispersion in the gap. Further, depending on cases, the magnetic suction force of the gap portion causes destruction of the core or scattering of debris of the core member.
In view of the above-described prior art, it is the problem of the present invention that in a transformer, (1) direct current magnetic deviation can be restrained without providing a gap in a core, (2) an increase in size or weight is not brought about, (3) an increase in the cost is not brought about.
It is an object of the present invention to provide a technology capable of resolving such problem.
In order to resolve the above-described problem, according to the present invention:
(1) There is constructed in such a manner that a transformer comprises a core for the transformer in which a B-H characteristic of a material characteristic in a direction along a magnetic circuit is brought into an unsaturated state and a primary side winding and a secondary side winding wound around the core for the transformer and the transformer is operated in the unsaturated region.
(2) There is constructed in such a manner that a transformer comprises a core for the transformer having an axis of easy magnetization in a second direction intersecting with a first direction along a magnetic circuit and a primary side winding and a secondary side winding wound around the core for the transformer.
(3) In the above-described (2), the core for the transformer is constituted by an amorphous metal.
(4) In the above-described (1) or (2), the core for the transformer is constituted by being laminated with core members each in a shape of a thin strip.
(5) In any of the above-described (2) through (4), the axis of easy magnetization of the core for the transformer is formed by applying a magnetic field in an annealing operation.
(6) There is provided a core for a transformer used in any of the transformers according to the above-described (1) through (5).
(7) As a method of fabricating a core for a transformer, the core for the transformer is fabricated after having been processed by a step of laminating core members each in a shape of a strip and forming the core members in a ring-like shape and a step of applying a direct current magnetic field in a direction intersecting with a direction along a magnetic circuit of the transformer to the formed core members in an annealing operation to thereby form an axis of easy magnetization of the core in a direction of the magnetic field.
(8) In the above-described (7), the direct current magnetic field is applied in a direction substantially orthogonal to the direction along the magnetic circuit of the transformer.
(9) As a method of fabricating a core for a transformer, the core of the transformer is fabricated after having been processed by a step of laminating core members each in a shape of a thin strip and forming the core members in a ring-like shape and a step of applying a direct current magnetic field in a first direction along a magnetic circuit of the transformer and a direct current magnetic field in a second direction intersecting with the first direction to the formed core members in an annealing operation to thereby form an axis of easy magnetization of the core in a direction of a magnetic field synthesized with the two magnetic fields.
(10) As a method of fabricating a core for a transformer, a core of a transformer is formed after having been processed by a step of subjecting core members to material taking from a magnetic material having an axis of easy magnetization substantially in a constant direction such that the axis of easy magnetization constitutes a direction intersecting with a direction along a magnetic circuit of the transformer and a step of laminating the core members.